The present application relates to GNSS (Global Navigation Satellite System) trajectory prediction.
Very precise knowledge of each of 3 or 4 GNSS satellites' clock and trajectory information is required to accurately calculate position of a remote receiver. The remote receiver can obtain this knowledge from the ephemeris information typically broadcasted repeatedly by each satellite every 30 seconds. However, due to many factors affecting the satellite's orbit, this broadcasted GNSS ephemeris information is typically only valid for 2 to 4 hours into the future.
Thus if a remote receiver has been unable to receive updated ephemeris information for an extended period, perhaps due to being turned off or disabled, any previously stored ephemeris information will be invalid when the remote receiver is reactivated, and updated information will be need to be retrieved from the satellites before the remote receiver can begin to calculate its current location. The delay in the remote receiver between being turned on and calculating current location is known as Time To First Fix (TTFF), and as any delay tends to frustrate a user, one of the most important tasks of a GNSS (e.g. GPS) is to speed up TTFF by extending or predicting the orbital ephemeris for the remote receiver.
One broad approach to this problem is for a server to collect ephemeris information and calculate extended satellite trajectory and clock information for many days into the future. Due to the complexity and required precision of orbital trajectory calculations, often using a perturbed Forced-model on received ephemeris information, the use of special software on a powerful central server is required to estimate extended trajectories for many days into the future while keeping estimations within acceptable error limits. Each time a remote receiver is reactivated, the remote receiver's TTFF can be shortened considerably by immediately receiving this extended information directly from the central server via an Internet or wireless communication system rather than waiting for the satellites to repeat their broadcast.
A second broad approach to the TTFF problem is for the server to continuously provide GNSS trajectory data that is valid for an extended period of time into the future on a mobile receiver. This solution requires the remote receiver to be in continuous or at least frequent connection with the server as well as adequate data storage capacity on the remote receiver.